Netbeans, indeed any Java compiler and
executor, needs to know the classpath
to compile and run a file. When you
just open a file in Netbeans, you do
not tell it any of that information.
When you set up a project, that
process tells Netbeans where the Java
resources are.

Yet other IDEs can easily do this. It's not good practice, but it's simple and quick for "fooling around".

Is there any way to compile & run a file, that doesn't belong to a project, in Netbeans?

edit: The options are greyed out if the file doesn't belong to a project.

3 Answers
3

Your best option with NetBeans is just to create a dummy "try stuff" project that you know will never contain a shipping product but will allow you to experiment without having to create a new project every time.

You could even collect code snippets in different classes this way. If you add a main() method to each experimental class, you have a way to run them all in the IDE just by changing what you have set for the main project class. This is what I do and it works pretty well.